Method and apparatus for manufacturing bent pipes

ABSTRACT

A method of manufacturing bent pipes which comprises melting a plurality of metal electrodes fed at a predetermined rate to an electroslag bath within a mold, allowing the molten metal thus formed to solidify to a shape conforming to the cross-sectional contour and curvature of a desired bent pipe, thereby forming a unitary bent pipe, and, at the same time, withdrawing said unitary bent pipe continuously along a curved path in agreement with the curvature of the desired bent pipe, and an apparatus adapted for the practice of the method.

United States Patent 11 1 Ujiie 1451 Nov. 27, 1973 [54] METHOD AND APPARATUS FOR 3,683,997 8 1972 Uziie et a1 164 52 MANUFACTURING BENT PIPES FOREIGN PATENTS OR APPLICATIONS lnvenwfl Akin i Kobe, Japan 1,281,115 10/1968 Germany 164/85 [73] Assignee: Mitsubishi Jukogyo Kabushiki Kaisha, Chiyoda, Tokyo, Japan Primary Examiner-J. Spencer Overholser Assistant ExaminerJohn E. Roethel [22] Flled: J 1971 Attorney-Toren 8c McGeady 21 Appl. No.: 152,854

[57] ABSTRACT [30] Foreign Application Priority Data A method Of manufacturing bent pipes which com- June 24, 1970 Japan 45/54354 prises melting plurality metal elecmdes fed a predetermined rate to an electroslag bath within a 52 US. 01 164/52, 164/85, 164 252 mold, allowing the molten metal thus formed to Solid 51 1111.111 B2241 27/02 ify ma ShaPe Conforming to the cross-Sectional [58] Field 61 Search 164/52, 85,252, and curvature of a desired bent P P thereby 164/231 forming a unitary bent pipe, and, at the same time, withdrawing said unitary bent pipe continuously along [56] Reterences Cited a curved path in agreement with the curvature of the UNITED STATES PATENTS desired bent pipe, and an apparatus adapted for the practice of the method. 3,610,319 10/1971 Klemhagauer eta] 164/252 10/1967 Tannann 164/85 2 Claims, 2 Drawing Figures METHOD AND APPARATUS FOR MANUFACTURING BENT PIPES This invention relates to a method of manufacturing bent pipes by melting metal electrodes fed to a mold in an electroslag bath therein, solidifying the molten metal in the mold, and continuously withdrawing the product from the mold to form a bent pipe with a desired curvature, and an apparatus for practicing the method.

Bent pipes with relatively high degrees of curvature, such as 180 and 90 bends, have usually been made by forging or casting. When forging is adopted for the manufacture of such a bent pipe, it not only involves the use of expensive dies but produces a bent pipe with irregularity in the curvature along the surfaces of the inner and outer radii and ununiformity in the wall thickness. Thus the product is questionable in quality. Particularly when the pipe is to be made of a material having relatively poor ductility, the pipe in the course of forging may develop cracks, fissures or other defects at its bent portion. Further, an increased degree of curvature or plastic working of the pipe could deteriorate the quality of the pipe material. In an effort to overcome such difficulties, it has been proposed and practiced to form by forging a plurality of split pipes with a relatively low degree of curvature and then unite them together to obtain a bent pipe with a desired curvature. The process again has problems of increased labor requirement and very high manufacturing cost. When casting is resorted to, instead, the bent pipe tends to have cavities and blowholes, the inevitable defects of a casting. These defects, if any, must be repaired with use of many man-hours, and therefore with added cost. For instance, in the petrochemicalindustry, the reaction tube such as a reformer bent tube, is madegf such ahigl grade steel as HK40 which cannot be forged but cast, and therefore the products are used only after meticulous repair work because of the possibility of the above-mentioned defects. Still, the pipe material of this type has too poor weldability for complete correction work, and the products are frequent source of complaints.

In view of the present state of the technology in the manufacture of bent pipes, the present invention has for an object to eliminate all the disadvantages of the conventional processes for producing bent pipes through adoption of unique technological means.

For the manufacture of straight pipes, a process is known whereby metal electrodes are fed in a mold having the same cross-sectional contour as the desired product and melted in an electroslag bath, and the mo]- ten metal thus obtained is solidified in the mold, and then the solidified metal is continuously withdrawn to form a lengthy straight pipe of a predetermined size. The process of manufacturing straight pipes in this way gives products relatively free from defects as compared with the other processes in use, and is particularly suitable for the .manufacture of straight pipes of high-grade steels. For this reason, the process is often employed, for example, for the fabrication of reaction tubes, such as reformer tubes, in the petrochemical industry.

Another object of the present invention is to provide a unique method and apparatus which, taking advantage of the above-described straight-pipe manufacturing process, incorporates the same for the manufacture of bent pipes.

Still another object of the invention is to provide a method of manufacturing bent pipes by melting a plurality of metal electrodes fed at a predetermined rate in an electroslag bath within a mold, solidifying the resulting molten metal in said mold, and then continuously withdrawing the solidified metal at a predetermined rate from the mold, characterized in that the molten metal in the mold is caused to solidify to a shape conforming to the cross-sectional contour and curvature of the desired bent pipe, thereby forming a unitary bent pipe, and, at the same time, the unitary bent pipe is continuously withdrawn along a curved path in agreement with the curvature of the desired bent pipe.

A further object of the invention is to provide an apparatus for manufacturing bent pipes comprising an electrode assembly which consists of a plurality of metal electrodes with different cross-sectional areas arranged substantially equidistantly to conform to the overall cross-sectional contour of the bent pipe to be made, from the inner radial side toward the outer radial side of the bent pipe, in the order of increasing crosssectional area of the electrodes, said metal electrodes being adapted to be brought down by suitable drives at a predetermined speed, mold members consisting of an outer mold and a water-cooled core both disposed immediately below said electrode assembly and defining therebetween an annular channel which has a suitable width and a gradually increasing depth from the inner radial side toward the outer radial side of the bent pipe to be made and also an annular hole which, in communication with said annular channel, has a width equal to the wall thickness of the pipe to be made and a gradually increasing depth from the inner radial side toward the outer radial side of the bent pipe and has a curvature equal to the curvature of said bent pipe, tumable members for withdrawing the bent pipe being formed consisting of an arm to be turned by suitable drives, and a start piece which is displaced by the turning of said arm along a curved path conforming to the curvature of said bent pipe for continuous withdrawal of the unitary bent pipe formed in said annular hole, and currentsupply members having terminals at one end which are connected to the metal electrodes through a currentcollecting board and a terminal at the other end which is connected to said arm of bent-pipe withdrawing turnable members.

With the apparatus above described, the method of the present invention for the manufacture of bent pipes can be smoothly reduced into practice.

The other advantages and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawing showing an embodiment of apparatus adapted for practicing the present invention. In the drawing:

FIG. 1 is a schematic view, in vertical section; and

FIG. 2 is a schematic plan view illustrating the crosssectional shapes and arrangement of metal electrode.

Referring now to the drawing, an electrode assembly is generally indicated at A. The electrode assembly A consists of groups of metal electrodes A A A A and A A A A and rollers a a a a a a a a (although only the rollers a and a, are shown in FIG. 1) which are driven by suitable drives (not shown) to bring down the electrodes at a predetermined speed. The electrodes are arranged, as better shown in FIG. 2, vertically and at equal distances from each other in a formation corresponding to the cross sectional contour of the bent pipe to be made. The crosssectional areas S, to S, and S, to S, of the metal electrodes A, to A, and A, to A,', respectively, are such that the cross-sectional areas 8,, S, of the metal electrodes A,, A, disposed on the side closest to the center of curvature of the bent pipe to be made are the smallest, and the cross-sectional areas 5,, S, of the metal electrodes A A, disposed on the side farthest from the center of curvature of the bent pipe to be formed are the largest. Thus the relations among these cross-sectional areas are S, S S S, and S, S S 8,, S 5,, and S, 8,.

Mold members B consist of an outer mold B, and a watercooled metal core 8,, both disposed immediately below the electrode assembly A. Between the outer mold B, and the core B is formed an annular channel W which is substantially funnel-shaped in vertical sec tion. In this annular channel W is formed a molten slag pool. The mold members B are disposed in such a way that the lower ends of the metal electrodes A, to A A, to A, rest in the center of the upper section of the annular channel W. The vertical sectional contours of the various portions of the annular channel'W are designed in consideration of the relations between the dimensions of the bent pipe to be made and the metal electrodes A, to A A, to A,.

In communication with the lower portion of the annular channel W there is defined an annular hole Y between the outer mold B, and the core B The annular hole Y is so formed as to have the same cross-sectional contour and also the same curvature as those of the bent pipe to be made. It permits the formation of the pool of molten metal M by the electroslag melt phenomenon of the metal electrodes A, to A A, to A, in the annular channel W. At the same time, it permits solidification of the molten metal by the chilling action of the mold members B, so that a unitary bent pipe AP can be continuously formed. The shape and dimensions of this annular hole Y are designed in conformity with the dimensions of the bent pipe to be made.

In FIG. 1 the symbol P designates a bent pipe with a wall thickness t to be made. Its curvature has an inner radius y, and an outer radius about an origin Q11;

s'ymboTOE indicates horizontal plane including the point Now, on the assumption that the manufacture of a bent pipe is started at a point advanced from the horizontal plane L by 0, the profiles of the annular channel W and the annular hole Y of the mold members B will be explained. In order to manufacture the bent pipe P by a center angle d6 per unit period of time, it is necessary to choose such dimensions for the mold members B that molten metal is collected in the portions eef' f and gg'h'h which are surrounded by the tions corresponding to 0 and 6+d6'from the origin 0 of FIG. 1, and the cross sections of the core B and the outer mold 8,, and the molten metal is cooled and solidified in said space to form the element AP of the bent pipe P. The portions below the portions ee' f f and gg'hh are gradually expanded, while the portions above the portions ee f f have the same radius up to the point i where the radius of y, z from f intersects 0L and up to the point j where the radius of y; from hintersects 0L. The portions above i, j and above e, g are gradually expanded so as to provide a suitable distance from the metal electrodes A, and A,. In FIGS. 1 and 2, the symbols 1, n, k, m indicate the points where the upper edge of the annular channel W intersects the line 5-8. The minimum distances from these points I, n, k, m to the metal electrodes A,, A, are the same. In this case the metal electrodes A,, A, are so arranged that their positions are on the vertical lines passing the points e, i', g, j. Further, a relationship ef= e'f gh g'h' =t is maintained. Although these relations have been described in connection with the section 5-8 of FIG. 2, it should be understood that the relations apply as well to the entire vertical section along the whole circumferences of the annular channel W and the annular hole Y.

The turnable members C for withdrawing the bent pipes being formed consist of an arm K attached to a shaft perpendicular to the paper and passing the point 0, ta pi c att d. t satlarm Kansans,

K is turned at a predetermined angular velocity by a motor (not shown) coupled to said vertical shaft. The start piece p is shaped to a unit length of the same dimensions as the bent pipe P to be made. It is displaced along a path having the same curvature as that of the bent pipe to be formed by the turning of the motordriven arm K, thereby to withdraw the element AP of the bent pipe P from the mold members B. When starting the manufacture of a bent pipe, the start piece p serves to close the bottom of the annular hole Y in the mold members B. An electric system D consists of an electroslag power source E and a current-collecting board F. A terminal at one end of the power source E is connected to the arm K, while the other terminals are electrically connected to the metal electrodes A, to A, and A, to A, of the electrode assembly A through the current-collecting board F.

When a bent pipe P is manufactured at a same angular velocity, or by withdrawing the bent pipe P by d0 per unit time, in accordance with this invention, the rate of melting of the metal electrodes A, to A, and A, to A, must be gradually increased from the portion eef f to the portion ggh'h of the annular hole Y. For this reason, under the invention, themetal electrodes A, to A, and A, to A, having different cross-sectional areas are melted simultaneously with the same voltage and the same current density, and the depth of the annular channel W wherein a slag pool is formed is gradually increased from the inner radial side toward the outer radial side of the curved. portion of the bent pipe being formed. Thus, although the unit current in the metal electrodes A, to A, and A, to A, is the same, the resistance varies and the melting effect of the metal electrodes is increased by the difference of R in PR, with the result that the metal electrodes give a desired amount of melt in the annular hole Y. For this purpose it is necessary, as noted above, to design the crosssectional areas S, to S, and S, to S, of the metal electrodes A, to A, and A, to A, and their arrangement suitably in conformity with the dimensions of the bent pipe P to be made and also to choose a suitable angle 6 and vary the value of the resistance R accordingly.

Description will now be made of the manufacture of a bent pipe P of a given metal material on the apparatus shown.

The metal electrodes A, to A, and A, to A, of the electrode assembly A in a given position are fed at a predetermined rate by rollers and brought down at a constant speed with a current supplied to the currentcollecting board F. In this case, the bottom of the annular hole Y isclosed beforehand with the start piece p, and suitable molten slag is held in the annular channel W. Then, the metal electrodes A to A and A, to A are immersed in molten slag pool, and these metal electrodes supply a current through the molten slag to the start piece p, thus forming an electric circuit for the power source E. In this way so-called electroslag melt phenomenon occurs, whereby the front end portions of the metal electrodes are melted combinedly to form the molten metal M, which in turn drops into the molten slag and is collected in the annular hole Y. This molten metal M is cooled and solidified by the mold B. At this time, the portion of the molten metal M in contact with the start piece p is fused to the start piece p. As soon as the molten metal is collected in the annular hole Y and begins solidification, the driving motor for the arm K runs at an angular velocity d6 per unit time to turn the arm K in the direction indicated by an arrow Z thereby to displace the start piece P in the direction of the arrow. As a result, the element AP of the bent pipe cooled and solidified by the mold B is gradually withdrawn from the mold B and a bent pipe P having a desired curvature is thereby formed.

With the construction and functions above described, the apparatus of the present invention continuously manufactures a bent pipe with a desired curvature directly from the molten metal that is obtained by melting in an electroslag bath a plurality of metal electrodes fed at a predetermined velocity in the mold. Therefore, not only a bent pipe of a desired material can be easily and promptly made but also a bent pipe free from any defect and far superior in quality to the conventional products can be made to great advantage.

I claim:

1. A method of manufacturing bent pipes which comprises the steps of feeding a plurality of metal electrodes to a mold at a predetermined rate and melting the same in an electroslag bath, solidifying the resulting molten metal to a size conforming to the desired crosssectional contour and curvature of the bent pipe to be formed, thereby forming a unitary bent pipe and, at the same time, continuously withdrawing said unitary bent pipe along a curved path in agreement with the curvature of said bent pipe, said steps being followed in a successive and sequential way, the plurality of metal electrodes being groups of metal electrodes having different cross-sectional areas, which are fed to the mold in an arrangement substantially at equal distances from one another and in the order of increasing crosssectional areas within the annular channel of the mold, the electrodes with small crosssectional areas being on the inner radial side of the curved portion of the bent pipe and the electrodes with larger cross-sectional areas on the outer radial side.

2. An apparatus for manufacturing bent pipes comprising an electrode assembly which consists of a plurality of metal electrodes with different cross-sectional areas arranged substantially equidistantly to conform to the overall cross-sectional contour of the bent pipe to be made, from the inner radial side toward the outer radial side of the bent pipe, in the order of increasing cross-sectional area of the electrodes, said metal electrodes being adapted to be brought down by suitable drives at a predetermined speed, mold members consisting of an outer mold and a water-cooled core both disposed immediately below said electrode assembly and defining therebetween an annular channel which has a suitable width and a gradually increasing depth from the inner radial side toward the outer radial side of the bent pipe to be made and also an annular hole which, in communication with said annular channel, has a width equal to the wall thickness of the pipe to be made and a gradually increasing depth from the inner radial side toward the outer radial side of the bent pipe and has a curvature equal to the curvature of said bent pipe, turnable members for withdrawing the bent pipe being formed consisting of an arm to be turned by suitable drives, and a start piece which is displaced by the turning of said arm along a curved path conforming to the curvature of said bent pipe for continuous withdrawal of the unitary bent pipe formed in said annular hole, and current-supply members having terminals at one end which are connected to the metal electrodes through a current-collecting board and a terminal at the other end which is connected to said arm of bentpipe withdrawing tumable members. 

1. A method of manufacturing bent pipes which comprises the steps of feeding a plurality of metal electrodes to a mold at a predetermined rate and melting the same in an electroslag bath, solidifying the resulting molten metal to a size conforming to the desired cross-sectional contour and curvature of the bent pipe to be formed, thereby forming a unitary bent pipe and, at the same time, continuously withdrawing said unitary bent pipe along a curved path in agreement with the curvature of said bent pipe, said steps being followed in a successive and sequential way, the plurality of metal electrodes being groups of metal electrodes having different cross-sectional areas, which are fed to the mold in an arrangement substantially at equal distances from one another and in the order of increasing cross-sectional areas within the annular channel of the mold, the electrodes with small cross-sectional areas being on the inner radial side of the curved portion of the bent pipe and the electrodes with larger cross-sectional areas on the outer radial side.
 2. An apparatus for manufacturing bent pipes comprising an electrode assembly which consists of a plurality of metal electrodes with different cross-sectional areas arranged substantially equidistantly to conform to the overall cross-sectional contour of the bent pipe to be made, from the inner radial side toward the outer radial side of the bent pipe, in the order of increasing cross-sectional area of the electrodes, said metal Electrodes being adapted to be brought down by suitable drives at a predetermined speed, mold members consisting of an outer mold and a water-cooled core both disposed immediately below said electrode assembly and defining therebetween an annular channel which has a suitable width and a gradually increasing depth from the inner radial side toward the outer radial side of the bent pipe to be made and also an annular hole which, in communication with said annular channel, has a width equal to the wall thickness of the pipe to be made and a gradually increasing depth from the inner radial side toward the outer radial side of the bent pipe and has a curvature equal to the curvature of said bent pipe, turnable members for withdrawing the bent pipe being formed consisting of an arm to be turned by suitable drives, and a start piece which is displaced by the turning of said arm along a curved path conforming to the curvature of said bent pipe for continuous withdrawal of the unitary bent pipe formed in said annular hole, and current-supply members having terminals at one end which are connected to the metal electrodes through a current-collecting board and a terminal at the other end which is connected to said arm of bent-pipe withdrawing turnable members. 